Observer agreement and accuracy in the evaluation of bone scans in newly diagnosed prostate cancer

OBJECTIVEThe aim of the study was to assess the agreement in the interpretation of bone scintigraphy (BS) in a newly diagnosed prostate cancer. MATERIALS AND METHODSA total of 635 consecutive patients had their planar whole-body BS independently reviewed by three nuclear medicine physicians and classified by two grading systems(a) a four-category scale (1benign; 2equivocal; 3most likely malignant; and 4multiple metastases) and (b) a dichotomous scale (bone metastasis present or absent). RESULTSAgreement in the same category, or with one or two categories of differences, was found in 66, 34, and 1.3% of the readings, respectively. Average κ-values were 0.59, 0.72, and 0.83 for unweighted, linear, and quadratic weighted variants, respectively. Very high agreement was observed (96% of the readings) with the dichotomous scale (average κ=0.87); a comparison with a final imaging diagnosis with additional CT or MRI showed a sensitivity of 83% and a specificity of 98%. BS categories 1, 3, and 4 were consistent with the final imaging diagnosis in 96–99% of cases. The prevalence of metastasis was 10% in category 2. To optimize the diagnostic characteristics, category 2 should be regarded as a separate option. CONCLUSIONClose agreement was found among trained observers for the evaluation of BS in prostate cancer. The high level of agreement with a dichotomous scale was hampered by diagnostic misclassification. A scale with equivocal findings on planar BS is considered important to allow for additional imaging and correct staging at the bone level of BS in a population with newly diagnosed prostate cancer.